Aging and Stereoscopic Shape Perception

Past research on stereoscopic depth perception among the elderly has led to inconsistent findings. Some research on stereopsis and aging has found that younger and older adults are essentially the same in terms of their stereoscopic ability, while other research has found evidence of large differences. This past research has largely been limited to investigations of stereoacuity. The purpose of Experiment 1 was to extend this earlier research to compare how older and younger observers perceive the magnitude of stereoscopically defined depth intervals. Random-dot stereograms depicting sinusoidal surfaces were shown to seven younger (i.e., ages 30 and below) and six older (i.e., ages 60 and above) adults. These surfaces were defined by three levels of peak-trough image disparity, two spatial frequencies, and two densities of texture elements. The observers\u27 task was to estimate the magnitude of the depth interval between the surfaces\u27 peaks and troughs. It was found that the perceived depth intervals of the younger observers were closer to those predicted by the geometry of stereopsis: as disparity increased, so did the magnitudes of their perceived depth intervals. This finding was also true for the five out of the six older adults, but the magnitudes of their perceived depth intervals were less than their younger counterparts. The high frequency surfaces were more difficult to perceive for both groups, but were especially difficult for the elderly. In contrast, texture element density had essentially no effect upon the observers\u27 performance for both groups. The results of this experiment showed that the elderly have a significant amount of stereoscopic functionality that is not qualitatively different from younger adults. Experiment 2 was designed to compare older and younger observers\u27 ability to perceive the shape of stereoscopic surfaces. In this experiment, four different surfaces defined by disparity (i.e., bumps, saddles, vertical cylinders, and horizontal cylinders) were shown to five younger (i.e., 30 and below) and five older (i.e., 60 and above) observers. The random-dot stereograms varied in terms of their texture element density and amount of correspondence. The results showed that the older observers were less sensitive to stereoscopic depth and curvature. In all other respects, however, the results for the older observers were essentially identical to those of the younger observers. In particular, the reductions in density and correspondence led to nearly identical declines in performance for both age groups. In summary, the results of both experiments showed that, despite some reductions in perceptual sensitivity, older adults can effectively perceive and discriminate the shape and depth of stereoscopic surfaces